1. Field of the Invention
The present invention relates to a method of washing petroleum equipment and a washing solution for use with the method.
2. Description of Related Art
Conventionally, it has been considered that water as well as surface-active agent are requisites for washing fluids used for washing petroleum equipment. When petroleum flows into sea, for example, surface-active agents are used to remove the petroleum because the surface-active agents can minutely disperse the petroleum in combination with seawater as a solvent.
As mentioned above, since water for the surface-active agent to be dispersed therein is a requisite for removing petroleum residue by the surface-active agent, it has been thought that the petroleum residue could not be removed by the surface-active agent in a waterless place.
However, in petroleum refining equipment, a part of petroleum is degraded to turn into macromolecule petroleum, which adheres on a wall of the equipment to be further firmly adhered (highly polymerized). The highly polymerized compound (referred to as petroleum residue hereinafter) becomes gradually thicker and thicker, which exerts bad influence on performance of the petroleum equipment. For instance, such petroleum residue significantly deteriorates heat exchange efficiency of the equipment.
Therefore, it is necessary to wash petroleum equipment for removing petroleum residue therefrom. However, when a water-containing washing solution is used, the petroleum equipment may be damaged or bad influence is caused on products on account of residual water. Accordingly, petroleum-rinsing or drying process has to be conducted after washing the petroleum equipment with the water-containing washing solution. As a result, the total equipment downtime is lengthened.
In the following description, the terms xe2x80x9cwashing solutionxe2x80x9d and xe2x80x9ccirculated washing solutionxe2x80x9d are equivalent and used interchangeably to denote a solution being circulated in petroleum equipment to wash petroleum residue or any other build-ups off the walls of the petroleum equipment.
The present invention has been reached based on the finding that surface-active agents are effective in finely dividing and dispersing the petroleum residue for removal, even in petroleum equipment having no water therein. In other words, washing solutions that contain no water can be used to effectively wash petroleum equipment.
A method of washing petroleum equipment according to an aspect of the present invention is characterized in using a compound of a surface-active agent and petroleum as a washing solution for the petroleum equipment.
A method of washing petroleum equipment according to another aspect of the present invention comprises the steps of:
a) preparing a non-aqueous washing solution consisting of a surface-active agent and petroleum, the petroleum comprising at least one selected from the group consisting of kerosene, light gas oil, vacuum gas oil and light cycle oil fraction;
b) introducing the washing solution inside the petroleum equipment; and
c) circulating the washing solution to wash the inside of the petroleum equipment.
Since the washing solution contains no water, there is no need for a rinsing or drying process as required by the conventional arrangement, thus simplifying the whole process and reducing the total downtime of the equipment.
The concentration of the surface-active agent in the washing solution is preferably from about 1 to about 20 volume percentage.
When the concentration of the surface-active agent is less than 1 volume percentage, the washing effect is significantly deteriorated. On the other hand, when the concentration of the surface-active agent exceeds 20 volume percentage, the washing effect increases only slightly, which does not justify the cost of the washing solution.
The temperature of the washing solution during the washing process is less than the boiling point of the solvent of the surface-active agent, which is preferably and normally between the normal temperature and 200xc2x0 C. The non-aqueous washing solution may preferably be heated while being circulated inside the petroleum equipment thus enhancing washing efficiency.
According to the method of the present invention, at least one property of the washing solution being circulated inside the petroleum equipment may preferably be monitored, and the concentration of the surface-active agent in the non-aqueous washing solution will preferably be adjusted, e.g., increased, when the monitored property or properties do not satisfy a predetermined standard.
The properties may be monitored in any suitable manner, such as visual observation of the washing solution and/or evaluation using a measuring device. The predetermined standard may be set in any manner, considering the type of the petroleum equipment to be washed, acceptable downtimes for the petroleum equipment, the properties of the washing solution etc.
The monitored properties of the non-aqueous washing solution preferably include at least one of the hue acid value and the residual carbon content of the circulated washing solution.
According to the method of the present invention, even when the non-aqueous washing solution does not show sufficient performance for washing the petroleum equipment at the initial stage of the washing process, the concentration of the surface-active agent can be adjusted, e.g., increased, during the washing process to attain desired washing efficiency.
In accordance with an embodiment of the present invention, a non-aqueous washing solution having a predetermined concentration, i.e., percentage by volume, of the surface-active agent may be directly introduced into the equipment and circulated therein until the end of the washing process without being changed or adjusted.
However, it is more preferable and flexible if the concentration of the surface-active agent in the non-aqueous washing solution can be adjusted during the washing process. For this purpose, an initial non-aqueous washing solution containing the surface-active agent of a concentration less that the predetermined concentration is first loaded into the equipment to be circulated therein. Thereafter, another, condensed non-aqueous washing solution having the surface-active agent of a concentration greater than the predetermined concentration is introduced in the petroleum equipment. Thus, a resulting washing solution which is a mixture of the initial non-aqueous washing solution and the condensed non-aqueous washing solution is circulated in the petroleum equipment. The resulting washing solution contains the surface-active agent of a concentration higher than the concentration of the initial washing solution but lower than the concentration of the condensed washing solution. Continually introducing the condensed washing solution into the petroleum equipment at, e.g., regular intervals will gradually increasing, or adjusting, the concentration of the surface-active agent in the resulting washing solution being circulated. Simultaneously, one or more properties of the circulated washing solution is/are being monitored for washing efficiency. When a desired washing effect has been reached, the introduction of the condensed washing solution is stopped. The introduction of the condensed washing solution may also be stopped when a maximum desired concentration of the surface-active agent, e.g., 20% by volume, in the circulated washing solution has been reached. The condensed washing solution and the initial washing solution preferably contain the same components, i.e., the same petroleum and surface-active agent, only in different concentrations.
Another embodiment of the present invention can be implemented in substantially the same manner as immediately described above, except that petroleum, instead of the initial washing solution, is introduced into the petroleum equipment. In other words, this embodiment is a particular case of the embodiment immediately described above when the initial washing solution contains no surface-active agent or has a zero concentration of the surface-active agent.
The condensed washing solution may preferably be loaded using injection equipment from a container of the condensed non-aqueous washing solution, with a pump and a pipe. However, when such injection equipment is not available, temporary injection equipment may be provided.
As mentioned above, when the condensed washing solution is used for conditioning/adjusting the concentration of the surface-active agent in the circulated non-aqueous washing solution, handling (such as manufacturing and transferring) of the washing solution can be facilitated, and the concentration of the surface-active agent in the circulated washing solution can be adjusted at an appropriate rate while checking the washing effect.
Especially, when it is necessary to gradually increase the concentration of the surface-active agent in the circulated washing solution, the concentration of the initial washing solution can be initially set low. Then, hue, acid value and residual carbon content of the circulated washing solution may be measured and, if the washing effect is low, the condensed washing solution can be additionally injected, thus easily conditioning the concentration of the circulated washing solution. Accordingly, excessive use of the surface-active agent can be prevented.
In accordance with the present invention, at least one of properties, including constituent thickness and solidness (i.e. consolidation, or hardness) of the petroleum residue inside the petroleum equipment may preferably be measured, and the concentration of surface-active agent in the circulated non-aqueous washing solution may preferably be adjusted in accordance with the measured properties of the petroleum residue.
According to the above arrangement, a non-aqueous washing solution containing a surface-active agent of an appropriate concentration can be introduced at the initial washing stage, thus enhancing washing efficiency.
Furthermore, the properties of petroleum residue and the corresponding concentrations of the surface-active agent in circulated non-aqueous washing solutions, that were sufficient to effectively remove the petroleum residue in previous washing cycles, may preferably be obtained and recorded. Then, in the next washing cycle, properties of the petroleum residue to be removed are measured, and compared with the previously recorded properties. The concentration of the surface-active agent in the circulated non-aqueous washing solution for the next washing cycle may preferably be adjusted to the recorded concentration that has been successfully applied in a previous cycle to remove petroleum residue that has recorded properties most proximate to the measured properties of the petroleum residue to be removed.
Accordingly, the most appropriate non-aqueous washing solution can be loaded in accordance with the results of previously conducted washing processes, thereby further enhancing the washing efficiency.
In addition, the temperature and/or the constituents or components of the circulated non-aqueous washing solution may preferably be adjusted in accordance with the monitored washing effect and properties of the petroleum residue.
The above petroleum equipment includes petroleum facility (heat exchanger, vessel, etc.), reactor filled with catalyst, desalter and tower as well as piping line.
A high boiling-point aromatic compound having a boiling point in the range of 150xc2x0 C. to 200xc2x0 C. may preferably be added in the washing solution of the present invention.
The high boiling-point aromatic compound includes single-ring and naphthalene ring compounds having one to three side chains of methyl base, ethyl base, propyl base etc.
The compounding ratio of the high boiling-point compound can be determined at will.
In the washing method of petroleum equipment according to the present invention, the surface-active agent may preferably be one selected from the group consisting of anionic surface-active agent, cationic surface-active agent, amphoteric surface-active agent and nonionic surface-active agent.
The anionic surface-active agent includes carboxylate, sulfonate, sulfate, phosphate etc.
The carboxylate includes ethanolamine soap, N-acyl amino acid, alkyl ether carboxylic acid etc.
The sulfonate includes alkylbenezene sulfonates, alkyl naphthalene sulfonates, melamine sulfonates, dialkyl sulfo-succinic acid, alkyl sulfo-aceitc acid, a-olefin sulfonic acid etc.
The sulfate ester salt includes sulfonated oil, higher alcohol sulfate, alkyl ether sulfuric acid, secondary higher alcohol ethoxy sulfuric acid, polyoxyethylene alkyl phenyl ether sulfuric acid, aliphatic alkylolamide sulfate etc.
The phosphoric ester salt is phosphoric ester such as alkylether phosphate ester, alkyl phosphoric acid ester.
The cationic surface-active agent is, for example, aliphatic amine such as aliphatic quaternary amine.
The amphoteric surface-active agent includes carboxy betaine, sulfo-betaine, amino carboxylate, imidazoline derivative, lecithin etc.
The nonionic surface-active agent includes ether type surface-active agent, ether-ester type surface-active agent, ester type surface surface-active agent, nitrogen-including surface-active agent etc.
The ether type surface-active agent includes polyoxyethylene alkyl ether, polyoxyethylene alcohol ether, polyoxyethylene alkyl phenyl ether etc.
The ether-ester type surface-active agent includes polyoxyethylene sorbitol aliphatic ester etc.
The ester type surface-active agent includes polyethylene glycol aliphatic ester etc.
The nitrogen-including nonionic surface-active agent includes fatty acid alkanolamide, polyoxyethylene fatty acid amide etc.
In the washing method of petroleum equipment according to the present invention, the surface-active agent may preferably be a combination of a nonionic surface-active agent and one selected from the group consisting of an anionic surface-active agent, a cationic surface-active agent and an amphoteric surface-active agent.
The nonionic surface-active agent, anionic surface-active agent, cationic surface-active agent, amphoteric surface-active agent are the same as those described above.
In the washing method of petroleum equipment according to the present invention, the petroleum may preferably be at least one selected from the group consisting of kerosene, light gas oil, vacuum gas oil and light cycle oil obtained from fluid catalystic cracking unit.
The kerosene is a fraction heavier than gasoline and lighter than light gas oil.
The light gas oil is a fraction of middle distillating product of crude distillation unit.
The vacuum gas oil is distillated oil obtained from vacuum distillation unit.
The light cycle oil is a fraction obtained from the fluid catalystic cracking unit.
In the washing method of petroleum equipment according to the present invention, the oil washing solution of the surface-active agent and oil may preferably include at least one of d-limonene and derivative thereof.
The derivative of d-limonene includes citral etc.
The compounding ratio of d-limonene may be determined at will.
By adding d-limonene into the washing solution, the solubility of the petroleum residue in the washing solution can be enhanced.
In the washing method of petroleum equipment according to the present invention, warm water may be used for further washing the equipment after washing using the non-aqueous washing solution.
The temperature of the warm water is preferably from about 30xc2x0 C. to about 90xc2x0 C.
After the washing process using a mixture of petroleum and a surface-active agent as the washing solution, the mixture is discharged.
The warm water washing may preferably be done after the washing process using the washing solution.
After the water washing process using warm water, the petroleum equipment may preferably be rinsed using a non-aqueous rinsing solution including or consisting of petroleum. Accordingly, undesirable influence caused by water can be prevented.
In the above water washing process, the warm water may preferably include a water-soluble surface-active agent.
An example of the water-soluble surface-active agent is alkylolamide sulfate, alkyl phosphoric acid ester etc. The surface-active agent may be a single compound or a combination of multiple compounds.
The concentration of the water-soluble surface-active agent in the non-aqueous rinsing solution may preferably be in the range from about 0.1 to about 5% by volume. When the concentration is less than 0.1% by volume, the washing effect is significantly deteriorated, and when the concentration exceeds 5% by volume, the cost for the surface-active agent unacceptably increases as compared to a slight increase in the washing efficiency.
The concentration of the water-soluble surface-active agent can be adjusted in the same manner as the surface-active agent used during the washing process.